The invention relates to a travel sensor.
In a travel sensor known from German Patent Disclosure DE OS 37 30 926, the motion of the piston of a cylinder, for instance in the control device for a rear-wheel drive of a motor vehicle, is detected. To that end, an extension of the piston comprising magnetizable material protrudes into a cylinder tube with coils with external windings, and by its motion leads to an inductive variation of the coil thread, which can be evaluated by measuring inventions.
A travel sensor described above is advantageous, because contactless travel measurement that is easily adaptable to different travel lengths can be realized in a simple way. Even to detect relatively long travel distances covered by a mechanical component, such as the brake pedal of a motor vehicle, a travel sensor with minimal installation space can be constructed by converting the longitudinal motion into a rotary motion.
Advantageously, the conversion of the longitudinal motion into a rotary motion can be done with a Bowden cable. This Bowden cable can easily be wound onto and unwound from the circumference of a circular rotatable sensor element that has a permanent magnet mounted on it. Any required restoring force for the Bowden cable is generated for instance with a spring, preferably a spiral spring, secured to the end of the Bowden cable and to the housing of the travel sensor.
In an advantageous embodiment, a revolution of the sensor module by an angle of greater than 180xc2x0 can also be detected, by providing that a second rotatable sensor element is present, driven with suitable speed reduction by the first sensor element. Each time the rotary angle of 180xc2x0 for the first sensor element is exceeded, an evaluatable signal is thus detectable in a simple way, and a travel measurement can be attained over a wide travel range with high resolution by measuring a rotary angle.
A simple realization of this travel measurement described above is effected in such a way that the first sensor element has a set of internal teeth, with which a set of external teeth of the second sensor element meshes, and that the ratio of the numbers of teeth of the two sets of teeth, or the diameters of the two sensor elements, is predetermined by the travel, to be detected, of the mechanical component.
For the contactless travel measurement with the detector according to the invention, reliable, redundant detection and evaluation even of the absolute value of the travel can advantageously be performed by generating an analog or digitized evaluation signal. To that end, existing techniques for contactless, high-resolution rotary angle detection can also be used.
For example, VDI-Bericht [Reports of the German Association of Engineers] No. 509 (VDI-Verlag 1984), pages 263-268, in the article entitled xe2x80x9cNeue, alternative Lxc3x6sungen fxc3xcr Drehzahlsensoren im Kraftfahrzeug auf magnetoresistiver Basisxe2x80x9d [Novel alternative solutions for magnetoresistive rpm sensors in the motor vehicle] describes how an especially simple and invulnerable rotary angle detection of rotating shafts or gear wheels can be performed, using magnetic probes as the sensor elements. This is possible because the field line direction of a permanent magnet located in the sensor can be varied and detected by means of a rotary motion. In the aforementioned previously known document, both magnetoresistive thin-film sensors and Hall elements are described as detectors, with which the scanning of a change in a magnetic field can be performed.